Deciphering the Role of BAG Proteins in Medulloblastoma: From Drug Resistance to Cell Fate Regulation

Medulloblastoma (MB) is the most common malignant pediatric brain tumor, with a significant percentage of patients (approximately 30%) experiencing tumor relapse despite aggressive multimodal therapy. Molecular classification defines four distinct MB subgroups: SHH, WNT, Group 3, and Group 4. However, rare histological entities such as Medullomyoblastoma (MMB), characterized by a combination of neuroectodermal and myoblast elements, cannot be categorized under this classification and are typically resistant to standard MB treatments. The emergence of chemoresistant cells, primarily through the overexpression of anti-apoptotic proteins such as the Bcl-2-associated athanogene (BAG) family, contributes to the high rate of tumor recurrence. This study had three primary aims: 1) to map the BAG family protein interactome in MB cells to guide future development of protein-protein inhibitors, 2) to design a novel BAG3 inhibitor to enhance MB cell sensitivity to chemotherapy and reduce recurrence, and 3) to investigate the unprecedented role of BAG6 as a regulator of cell fate in MB. Our interactome study revealed novel BAG-related interactions, identifying new potential therapeutic targets. Additionally, we discovered a novel BAG3 inhibitor, FB49, which demonstrated high affinity for BAG3 and significant antiproliferative activity in MB cells. FB49-induced BAG3 inhibition led to cell cycle arrest, apoptosis, and autophagy. Notably, inhibiting BAG3-mediated autophagy enhanced the cytotoxic effects of FB49, revealing promising therapeutic opportunities in combination with standard chemotherapy. Furthermore, this study sheds light on the novel role of BAG6 in MB pathogenesis. BAG6 depletion was found to induce drug tolerance and modulate expression of both stemness (Sox2, Nanog, Oct4) and neural progenitor markers (βIII-tubulin, NeuroD1, Nestin), driving MB cells into a transit-amplifying progenitor state. BAG6-depleted cells exhibited enhanced proliferative capacity, elevated C-Myc expression, and the ability to reprogram MB cells toward a muscle cell fate, mimicking MMB pathology. These findings suggest that BAG6 functions as a tumor suppressor and may play a critical role in the development of rare and aggressive MMB variants. Collectively, our results provide valuable insights into BAG family proteins as therapeutic targets in MB and MMB, offering new avenues for drug development.